Cefotaximases (CTX-M-ases), an expanding family of extended-spectrum β-lactamases

Extended spectrum beta-lactamase carriage among elderly residents of a long-term care facility in Beirut

BACKGROUND

Antimicrobial resistance is an emerging problem worldwide, endangering antimicrobials efficacy and resulting in high rates of morbidity and mortality. It is one of the major concerns that health care facilities are facing nowadays. Mainly, extended-spectrum beta-lactamases (ESBL)-producing Enterobacterales play a role in hydrolyzing β-lactams, specifically the third-generation cephalosporins. This study aimed to investigate the prevalence of fecal carriage and molecular characterization of ESBL-producing Enterobacterales among Lebanese elderly residents in a long-term care facility (Dar Al-Ajaza Al Islamia Hospital).

METHODS

Rectal culture swab specimens were collected from 132 patients at Dar Al Ajaza Al Islamia hospital between January 2019 till June 2020. The phenotype of ESBL producers was confirmed by a modified double disc synergy test and antibiotic susceptibility was determined using the Kirby-Bauer disk diffusion method. Genotypically, multiplex polymerase chain reaction was used to detect the ESBL genes.

RESULTS

The main Enterobacterales strain observed was E coli (90.15%) followed by Klebsiella pneumoniae (4.54%) and Klebsiella oxytoca (3.80%). It has been found that the ESBL percentage rate has decreased when compared to a study conducted previously at the same hospital. Moreover, the predominant ESBL gene was CTX-M (cefotaximase).

CONCLUSIONS

This study is the first to demonstrate the improved current status of ESBL in one long-term care facility. In addition, the CTX-M is still the major type in ESBL-producing organisms.

ESBL-Producing Enterobacterales at the Human-Domestic Animal-Wildlife Interface: A One Health Approach to Antimicrobial Resistance in Piauí, Northeastern Brazil

The use, misuse, and overuse of antimicrobials is one of the main public health threats of the 21st century. We investigated the risk factor of the presence of extended-spectrum, cephalosporin-resistant Enterobacterales in feces of non-domestic and domestic birds and other domestic animals in Piauí State, northeast Brazil. We collected a total of 387 cloacal and rectal swab samples of free-living birds, domestic birds, and domestic mammals in five municipalities: Amarante, Água Branca, Lagoa Alegre, Parnaíba, and Teresina. A total of 59/387 (15.2%) of these samples harbored extended spectrum beta-lactamase (ESBL)-producing Enterobacterales. Using the MALDI-TOF technique, we identified fifty-seven samples as Escherichia coli and two samples as Klebsiella pneumoniae. Teresina and Parnaíba had the highest prevalence of animals with resistant bacteria (32.1% and 27.1%, respectively) and highest exposure risk factor (OR of 16.06 and 8.58, respectively, and p < 0.001 for all). Multidrug-resistant, ESBL-producing Enterobacterales were observed in 72.8% of the samples (43/59). For the free-living birds, the positive samples belonged to a great kiskadee (Pitangus sulphuratus) and a semipalmated sandpiper (Calidris pusilla) in migratory and resident species, respectively. For domestic animals, the swine samples showed the highest prevalence of antimicrobial resistance. The lack of access to veterinary care and information regarding antimicrobial therapy, along with the easy access to antimicrobials without medical prescription, favors the inadequate use of antimicrobials in Piauí.

Defying the odds: Determinants of the antimicrobial response of Salmonella Typhi and their interplay

Salmonella Typhi, the invasive serovar of S. enterica subspecies enterica, causes typhoid fever in healthy human hosts. The emergence of antibiotic-resistant strains has consistently challenged the successful treatment of typhoid fever with conventional antibiotics. Antimicrobial resistance (AMR) in Salmonella is acquired either by mutations in the genomic DNA or by acquiring extrachromosomal DNA via horizontal gene transfer. In addition, Salmonella can form a subpopulation of antibiotic persistent (AP) cells that can survive at high concentrations of antibiotics. These have reduced the effectiveness of the first and second lines of antibiotics used to treat Salmonella infection. The recurrent and chronic carriage of S. Typhi in human hosts further complicates the treatment process, as a remarkable shift in the immune response from pro-inflammatory Th1 to anti-inflammatory Th2 is observed. Recent studies have also highlighted the overlap between AP, persistent infection (PI) and AMR. These incidents have revealed several areas of research. In this review, we have put forward a timeline for the evolution of antibiotic resistance in Salmonella and discussed the different mechanisms of the same availed by the pathogen at the genotypic and phenotypic levels. Further, we have presented a detailed discussion on Salmonella antibiotic persistence (AP), PI, the host and bacterial virulence factors that can influence PI, and how both AP and PI can lead to AMR.

Cefepime in vivo activity against carbapenem-resistant Enterobacterales that test as cefepime susceptible or susceptible-dose dependent in vitro: implications for clinical microbiology laboratory and clinicians

BACKGROUND

Carbapenem-resistant Enterobacterales (CRE) are a public health concern. Among these isolates, there are reports of isolates that test as cefepime susceptible or susceptible-dose dependent (SDD) in vitro despite presence of a carbapenemase. This study aimed to evaluate the pharmacokinetic/pharmacodynamic profile of cefepime against carbapenemase-producing (CP-CRE) and non-producing (non-CP-CRE) isolates with a range of cefepime MICs.

METHODS

Reference broth microdilution and modified carbapenem inactivation method (mCIM) were performed on genotypically characterized clinical CRE isolates. Ultimately, CP-CRE (n = 21; blaKPC) and non-CP-CRE (n = 19) isolates with a distribution of cefepime MICs (≤0.5 to >256 mg/L) were utilized in the murine thigh infection model. Mice were treated with cefepime human-simulated regimens (HSRs) representative of a standard dose (1 g q12h 0.5 h infusion) or the SDD dose (2 g q8h 0.5 h infusion). Efficacy was assessed as the change in bacterial growth at 24 h compared with 0 h control, where ≥1 log bacterial reduction is considered translational value for clinical efficacy.

RESULTS

Among both cohorts of CRE isolates, i.e. CP-CRE and non-CP-CRE, that tested as SDD to cefepime in vitro, 1 log bacterial reduction was not attainable with cefepime. Further blunting of cefepime efficacy was observed among CP-CRE isolates compared with non-CP-CRE across both susceptible and SDD categories.

CONCLUSIONS

Data indicate to avoid cefepime for the treatment of serious infections caused by CRE isolates that test as cefepime susceptible or SDD. Data also provide evidence that isolates with the same antibiotic MIC may have different pharmacokinetic/pharmacodynamic profiles due to their antimicrobial resistance mechanism.

Membrane Efflux Pumps of Pathogenic Vibrio Species: Role in Antimicrobial Resistance and Virulence

Infectious diseases caused by bacterial species of the Vibrio genus have had considerable significance upon human health for centuries. V. cholerae is the causative microbial agent of cholera, a severe ailment characterized by profuse watery diarrhea, a condition associated with epidemics, and seven great historical pandemics. V. parahaemolyticus causes wound infection and watery diarrhea, while V. vulnificus can cause wound infections and septicemia. Species of the Vibrio genus with resistance to multiple antimicrobials have been a significant health concern for several decades. Mechanisms of antimicrobial resistance machinery in Vibrio spp. include biofilm formation, drug inactivation, target protection, antimicrobial permeability reduction, and active antimicrobial efflux. Integral membrane-bound active antimicrobial efflux pump systems include primary and secondary transporters, members of which belong to closely related protein superfamilies. The RND (resistance-nodulation-division) pumps, the MFS (major facilitator superfamily) transporters, and the ABC superfamily of efflux pumps constitute significant drug transporters for investigation. In this review, we explore these antimicrobial transport systems in the context of Vibrio spp. pathogenesis and virulence.

The role of tazobactam-based combinations for the management of infections due to extended-spectrum β-lactamase-producing Enterobacterales: Insights from the Society of Infectious Diseases Pharmacists

Extended-spectrum β-lactamase (ESBL)-producing Enterobacterales are a global threat to public health due to their antimicrobial resistance profile and, consequently, their limited available treatment options. Tazobactam is a sulfone β-lactamase inhibitor with in vitro inhibitory activity against common ESBLs in Enterobacterales, including CTX-M. However, the role of tazobactam-based combinations in treating infections caused by ESBL-producing Enterobacterales remains unclear. In the United States, two tazobactam-based combinations are available, piperacillin-tazobactam and ceftolozane-tazobactam. We evaluated and compared the roles of tazobactam-based combinations against ESBL-producing organisms with emphasis on pharmacokinetic/pharmacodynamic exposures in relation to MIC distributions and established breakpoints, clinical outcomes data specific to infection site, and considerations for downstream effects with these agents regarding antimicrobial resistance development. While limited data with ceftolozane-tazobactam are encouraging for its potential role in infections due to ESBL-producing Enterobacterales, further evidence is needed to determine its place in therapy. Conversely, currently available microbiologic, pharmacokinetic, pharmacodynamic, and clinical data do not suggest a role for piperacillin-tazobactam, and we caution clinicians against its usage for these infections.

Structural Comparisons of Cefotaximase (CTX-M-ase) Sub Family 1

The cefotaximase or CTX-M, family of serine-β-lactamases represents a significant clinical concern due to the ability for these enzymes to confer resistance to a broad array of β-lactam antibiotics an inhibitors. This behavior lends CTX-M-ases to be classified as extended spectrum β-lactamases (ESBL). Across the family of CTX-M-ases most closely related to CTX-M-1, the structures of CTX-M-15 with a library of different ligands have been solved and serve as the basis of comparison within this review. Herein we focus on the structural changes apparent in structures of CTX-M-15 in complex with diazabicyclooctane (DABCO) and boronic acid transition state analog inhibitors. Interactions between a positive surface patch near the active site and complementary functional groups of the bound inhibitor play key roles in the dictating the conformations of active site residues. The insights provided by analyzing structures of CTX-M-15 in complex with DABCO and boronic acid transition state analog inhibitors and analyzing existing structures of CTX-M-64 offer opportunities to move closer to making predictions as to how CTX-M-ases may interact with potential drug candidates, setting the stage for the further development of new antibiotics and β-lactamase inhibitors.

Extended-spectrum β-lactamases: an update on their characteristics, epidemiology and detection

Extended-spectrum β-lactamase (ESBL)-producing Gram-negative pathogens are a major cause of resistance to expanded-spectrum β-lactam antibiotics. Since their discovery in the early 1980s, they have spread worldwide and an are now endemic in Enterobacterales isolated from both hospital-associated and community-acquired infections. As a result, they are a global public health concern. In the past, TEM- and SHV-type ESBLs were the predominant families of ESBLs. Today CTX-M-type enzymes are the most commonly found ESBL type with the CTX-M-15 variant dominating worldwide, followed in prevalence by CTX-M-14, and CTX-M-27 is emerging in certain parts of the world. The genes encoding ESBLs are often found on plasmids and harboured within transposons or insertion sequences, which has enabled their spread. In addition, the population of ESBL-producing Escherichia coli is dominated globally by a highly virulent and successful clone belonging to ST131. Today, there are many diagnostic tools available to the clinical microbiology laboratory and include both phenotypic and genotypic tests to detect β-lactamases. Unfortunately, when ESBLs are not identified in a timely manner, appropriate antimicrobial therapy is frequently delayed, resulting in poor clinical outcomes. Several analyses of clinical trials have shown mixed results with regards to whether a carbapenem must be used to treat serious infections caused by ESBLs or whether some of the older β-lactam-β-lactamase combinations such as piperacillin/tazobactam are appropriate. Some of the newer combinations such as ceftazidime/avibactam have demonstrated efficacy in patients. ESBL-producing Gram-negative pathogens will continue to be major contributor to antimicrobial resistance worldwide. It is essential that we remain vigilant about identifying them both in patient isolates and through surveillance studies.

Non-carbapenem antimicrobial therapy in young infant with urinary tract infections caused by community-acquired extended-spectrum β-lactamase-producing Escherichia coli

BACKGROUND

The frequency of urinary tract infections (UTIs) caused by community-acquired extended-spectrum β-lactamase (CA-ESBL)-producing Enterobacteriaceae is increasing worldwide. Increased carbapenem use may lead to selection of carbapenem-resistant organisms, resulting in dire consequences for hospitals. We compared the outcomes of non-carbapenem antimicrobial therapy on UTIs caused by CA-ESBL-producing and non-producing Escherichia coli (E. coli) in infants younger than 6 months of age.

METHODS

We conducted a retrospective chart review, from January 2010 to December 2018, in infants (0-6 months old) with diagnosed UTIs caused by CA-ESBL-producing and non-producing E. coli at the Pusan National University Children's Hospital. Chart reviews were completed for patients whose urine sample had been collected using urinary catheterization. We treated all patients using non-carbapenem antimicrobials. Two weeks after therapy completion, clinical states were evaluated.

RESULTS

There were 105 and 582 patients diagnosed with UTIs caused by CA-ESBL-producing and non-producing E. coli, respectively. The mean age at diagnosis in ESBL and non-ESBL groups was 2.7 ± 1.6 and 2.8 ± 1.1 months (P = 0.711), respectively. There were no significant differences between ESBL and non-ESBL groups in the duration of fever (1.2 ± 0.5 and 1.2 ± 0.4 days, respectively, P = 0.761) or clinical cure states post therapy (101/105 and 567/582, respectively, P = 0.513).

CONCLUSION

This study found no significant differences in treatment outcomes between ESBL and non-ESBL groups treated with non-carbapenem antimicrobials. Therefore, initially administered non-carbapenem antimicrobials can be continued in patients with UTIs caused by CA-ESBL-producing E. coli who show clinical improvement.

Acinetobacter baumannii Antibiotic Resistance Mechanisms

Acinetobacter baumannii is a Gram-negative ESKAPE microorganism that poses a threat to public health by causing severe and invasive (mostly nosocomial) infections linked with high mortality rates. During the last years, this pathogen displayed multidrug resistance (MDR), mainly due to extensive antibiotic abuse and poor stewardship. MDR isolates are associated with medical history of long hospitalization stays, presence of catheters, and mechanical ventilation, while immunocompromised and severely ill hosts predispose to invasive infections. Next-generation sequencing techniques have revolutionized diagnosis of severe A. baumannii infections, contributing to timely diagnosis and personalized therapeutic regimens according to the identification of the respective resistance genes. The aim of this review is to describe in detail all current knowledge on the genetic background of A. baumannii resistance mechanisms in humans as regards beta-lactams (penicillins, cephalosporins, carbapenems, monobactams, and beta-lactamase inhibitors), aminoglycosides, tetracyclines, fluoroquinolones, macrolides, lincosamides, streptogramin antibiotics, polymyxins, and others (amphenicols, oxazolidinones, rifamycins, fosfomycin, diaminopyrimidines, sulfonamides, glycopeptide, and lipopeptide antibiotics). Mechanisms of antimicrobial resistance refer mainly to regulation of antibiotic transportation through bacterial membranes, alteration of the antibiotic target site, and enzymatic modifications resulting in antibiotic neutralization. Virulence factors that may affect antibiotic susceptibility profiles and confer drug resistance are also being discussed. Reports from cases of A. baumannii coinfection with SARS-CoV-2 during the COVID-19 pandemic in terms of resistance profiles and MDR genes have been investigated.

Can the use of older-generation beta-lactam antibiotics in livestock production over-select for beta-lactamases of greatest consequence for human medicine? An in vitro experimental model

Though carbapenems are not licensed for use in food animals in the U.S., carbapenem resistance among Enterobacteriaceae has been identified in farm animals and their environments. The objective of our study was to determine the extent to which older-generation β-lactam antibiotics approved for use in food animals in the U.S. might differentially select for resistance to antibiotics of critical importance to human health, such as carbapenems. Escherichia coli (E. coli) strains from humans, food animals, or the environment bearing a single β-lactamase gene (n = 20 each) for blaTEM-1, blaCMY-2, and blaCTX-M-* or else blaKPC/IMP/NDM (due to limited availability, often in combination with other bla genes), were identified, along with 20 E. coli strains lacking any known beta-lactamase genes. Baseline estimates of intrinsic bacterial fitness were derived from the population growth curves. Effects of ampicillin (32 μg/mL), ceftriaxone (4 μg/mL) and meropenem (4 μg/mL) on each strain and resistance-group also were assessed. Further, in vitro batch cultures were prepared by mixing equal concentrations of 10 representative E. coli strains (two from each resistance gene group), and each mixture was incubated at 37°C for 24 hours in non-antibiotic cation-adjusted Mueller-Hinton II (CAMH-2) broth, ampicillin + CAMH-2 broth (at 2, 4, 8, 16, and 32 μg/mL) and ceftiofur + CAMH-2 broth (at 0.5, 1, 2, 4, and 8μg/mL). Relative and absolute abundance of resistance-groups were estimated phenotypically. Line plots of the raw data were generated, and non-linear Gompertz models and multilevel mixed-effect linear regression models were fitted to the data. The observed strain growth rate distributions were significantly different across the groups. AmpC strains (i.e., blaCMY-2) had distinctly less robust (p < 0.05) growth in ceftriaxone (4 μg/mL) compared to extended-spectrum beta-lactamase (ESBL) producers harboring blaCTX-M-*variants. With increasing beta-lactam antibiotic concentrations, relative proportions of ESBLs and CREs were over-represented in the mixed bacterial communities; importantly, this was more pronounced with ceftiofur than with ampicillin. These results indicate that aminopenicillins and extended-spectrum cephalosporins would be expected to propagate carbapenemase-producing Enterobacteriaceae in food animals if and when Enterobacteriaceae from human health care settings enter the food animal environment.

Prevalence of Extended-Spectrum β-lactamases in Enterobacteriaceae Isolated from Polluted Wild Fish

Background:

Antibiotic resistance is becoming a major public health concern worldwide. In marine animals, pollution is associated with the emergence of extended-spectrum β-lactamase (ESBL)-expressing bacteria, resulting in antibiotic resistance. However, the prevalence of these bacteria in wild fish has not been reported.

Objective:

Accordingly, in this study, we explored the influence of pollution oxidative stress on the incidence of ESBL-expressing Enterobacteriaceae in the gut of wild fish species from the Red Sea coastal region of Jeddah City, Saudi Arabia. Additionally, we evaluated the incidence of varied ESBL genes contributing to the ESBL+ phenotype.

Methods:

Antibiotic susceptibility tests were performed using cephalosporins and carbapenems against ESBL- and carbapenem-resistant Enterobacteriaceae (CRE)-producing bacteria. Frequent genes contributing to the ESBL+ phenotype were analyzed. Primers targeting ESBLs (e.g., blaCTX, blaSHV, blaTEM, and blaOXA) were used in polymerase chain reaction assays to detect the ESBL+ phenotype.

Results:

Screening results from the polluted site revealed ESBL-resistant Klebsiella pneumoniae B8 and CRE-resistant Morganella morganii A4. The evolution of the blaCTX-M gene in M. morganii was a consequence of aquatic pollution. The other isolates Acinetobacter pittii and Providencia rettgeri were found in the clean reference site. The isolate M. morganii showed resistance to most mutual antibiotics and expressed some β-lactamase genes.

Conclusion:

Our findings provide useful data for selecting marine molecular genomic biomarkers caused by aquatic pollution.

Novel clinically relevant antibiotic resistance genes associated with sewage sludge and industrial waste streams revealed by functional metagenomic screening

A growing body of evidence indicates that anthropogenic activities can result in increased prevalence of antimicrobial resistance genes (ARGs) in bacteria in natural environments. Many environmental studies have used next-generation sequencing methods to sequence the metagenome. However, this approach is limited as it does not identify divergent uncharacterized genes or demonstrate activity. Characterization of ARGs in environmental metagenomes is important for understanding the evolution and dissemination of resistance, as there are several examples of clinically important resistance genes originating in environmental species. The current study employed a functional metagenomic approach to detect genes encoding resistance to extended spectrum β-lactams (ESBLs) and carbapenems in sewage sludge, sludge amended soil, quaternary ammonium compound (QAC) impacted reed bed sediment and less impacted long term curated grassland soil. ESBL and carbapenemase genes were detected in sewage sludge, sludge amended soils and QAC impacted soil with varying degrees of homology to clinically important β-lactamase genes. The flanking regions were sequenced to identify potential host background and genetic context. Novel β-lactamase genes were found in Gram negative bacteria, with one gene adjacent to an insertion sequence ISPme1, suggesting a recent mobilization event and/ the potential for future transfer. Sewage sludge and quaternary ammonium compound (QAC) rich industrial effluent appear to disseminate and/or select for ESBL genes which were not detected in long term curated grassland soils. This work confirms the natural environment as a reservoir of novel and mobilizable resistance genes, which may pose a threat to human and animal health.

Distribution and molecular characterization of beta-lactamases in Gram-negative bacteria in Colombia, 2001-2016

Beta-lactamases are enzymes with hydrolytic activity over beta-lactam antibiotics and they are the main resistance mechanism in Gram-negative bacteria. Extended-spectrum beta-lactamases (ESBL), AmpC, and carbapenemases have the greatest clinical and epidemiological impact in hospital settings. The increasing frequency and worldwide spread of these enzymes have limited the therapeutic options in hospital-acquired infections and those originating in the community. In Colombia, surveillance networks and research groups began studying them in the late 90s. Different variants of these enzymes have been molecularly characterized and their high prevalence and dissemination in medium and high complexity hospitals, along with a high clinical impact, have been reported. Furthermore, many studies in Colombia have evidenced high endemicity for some of these beta-lactamases, which requires an urgent implementation of antimicrobial stewardship programs in order to preserve the few therapeutic options and infection control strategies to prevent and limit their dissemination. In this publication, we carried out a review of the different enzyme variants, geographic distribution, and molecular characterization of these beta-lactamases in Colombia. Additionally, we describe the available information in the literature regarding studies conducted between the late 1990s and 2016, which provide an overview of the beta-lactamases circulating in different regions of Colombia, their increase over time, and their clinical implications.

Detection of blaCTX-M Extended Spectrum Beta-lactamase Producing Salmonella enterica Serotype Typhi in a Tertiary Care Centre

Introduction

Infections caused by Salmonella are an important public health threat in tropical and subtropical countries. Due to the emergence of resistance to ampicillin, chloramphenicol and trimethoprim/sulfamethoxazole (multidrug resistant salmonellae) in the late 1980s, fluoroquinolones and extended spectrum cephalosporins became the drugs of choice. Resistance to cefotaxime and ceftriaxone due to the production of Extended Spectrum Beta-Lactamase (ESBL) and reduced susceptibility to ciprofloxacin have emerged resulting in treatment failure. The Cefotaximase (CTX-M) type ESBLs are the most widespread beta lactamase among Enterobacteriaceae including salmonellae.

Aim

To detect the presence of bla_CTX-M in salmonellae causing human infections. Detection of qnr genes to identify the coexistence of bla_CTX-M and qnr gene.

Materials and Methods

The study included 103 consecutive, non-repetitive salmonellae isolated from clinical specimens obtained from July 2015- June 2016 which were identified up to species level by conventional/automated methods. Susceptibility to various classes of antimicrobial agents was determined by disc diffusion method. Minimum Inhibitory Concentration (MIC) to cefotaxime and ceftriaxone was determined by agar dilution method. The results were interpreted in accordance with Clinical & Laboratory Standard Institute (CLSI) (guidelines 2015. Detection of the ESBL phenotype was performed by the combined disk method. Polymerase Chain Reaction (PCR) amplification of all isolates was performed using group specific primers to characterize the presence of bla_CTX-M, qnrA, qnrB and qnrS.

Result

Of the 103 study isolates two isolates of Salmonella typhi were resistant to cefotaxime and ceftriaxone and had a MIC of 128μg/ml. PCR amplification and sequencing detected the presence of bla_CTX-M-15 in these two isolates. These two isolates exhibited resistance to ciprofloxacin in vitro but qnr gene was not detected in these isolates.

Conclusion

Resistance to third generation cephalosporins among salmonellae is a cause for concern as it may lead to treatment failure. It is imperative to continuously monitor the susceptibility pattern as enteric fever is endemic in India.

Molecular investigation of extended-spectrum beta-lactamase genes and potential drug resistance in clinical isolates of Morganella morganii

BACKGROUND

Resistance to beta-lactam antibiotics has become more common in Morganella morganii, which can cause of outbreaks of bacteremia and septicemia in postoperative patients.

OBJECTIVE

Investigate drug susceptibility of M morganii, identify the gene responsible for extended-spectrum beta-lactamase (ESBL) production and explore treatment options.

DESIGN

Descriptive study.

SETTING

Hospitals in An Najaf, Iraq.

METHODS

M morganii isolates were identified based on morphology, biochemical tests and VITEK® 2 compact system using (GN-ID) card. M morganii isolates were subjected to antibiotic resistance tests using the minimum inhibitory concentration (MIC) technique and an antibiogram was produced. Molecular studies were conducted using the polymerase chain reaction technique.

MAIN OUTCOME MEASURE(S)

Minimum inhibitory concentration.

RESULTS

From 395 gram-negative bacteria, only 17 isolates M morganii grew on MacConkey agar. M morganii isolates strongly resistant to several antibiotics were considered multidrug resistant. All M morganii isolates were ESBL producers. Four genes (CTX-M, SHV, TEM and OXA) encoding the b-lactamase enzyme were detected. Meropenem and imipenem were highly active against the M morganii isolates.

CONCLUSIONS

All isolates showed resistance to most common antibiotics, which limits options for treatment. This study provided useful information for selecting antibiotics to precisely target infections caused by M morganii.

LIMITATIONS

Limited to antibiotic susceptibility and genotype.

Microbial interaction between a CTXM-15 -producing Escherichia coli and a susceptible Pseudomonas aeruginosa isolated from bronchoalveolar lavage: influence of cefotaxime in the dual-species biofilm formation

Two isolates, Escherichia coli ella00 and Pseudomonas aeruginosa ella01, obtained from bronchoalveolar lavage, were found to be closely associated in clusters in agar medium. Escherichia coli ella00 was multidrug resistant and CTXM-15 extended-spectrum β-lactamase producer, while P. aeruginosa ella01 was susceptible to all antimicrobials tested. These observations impelled for further studies aimed to understand their microbial interaction. The P. aeruginosa ella01 biofilm-forming capacity was reduced and not affected when it was co-cultured with E. coli ella00 and E. coli ATCC 25922 respectively. Interestingly, the co-culture of ella isolates in the presence of high concentrations, such as 160 μg ml(-1) , of cefotaxime allowed the formation of more biofilm than in the absence of the antibiotic. As revealed by fluorescence in situ hybridization, in co-culture, P. aeruginosa ella01 survived and subsequently flourished when exposed to this third-generation cephalosporin at a concentration 10 × higher than its minimum inhibitory concentration (MIC), and this was mostly due to β-lactamases production by E. coli ella00. In fact, it was demonstrated by high-performance liquid chromatography that cefotaxime was absent for the culture medium 4 h after application. In conclusion, we demonstrate that bacterial species can interact differently depending on the surrounding conditions (favourable or stressing), and that those interactions can switch from unprofitable to beneficial.

Urinary tract infections: epidemiology, mechanisms of infection and treatment options

Urinary tract infections (UTIs) are a severe public health problem and are caused by a range of pathogens, but most commonly by Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Enterococcus faecalis and Staphylococcus saprophyticus. High recurrence rates and increasing antimicrobial resistance among uropathogens threaten to greatly increase the economic burden of these infections. In this Review, we discuss how basic science studies are elucidating the molecular details of the crosstalk that occurs at the host-pathogen interface, as well as the consequences of these interactions for the pathophysiology of UTIs. We also describe current efforts to translate this knowledge into new clinical treatments for UTIs.

Code blue: Acinetobacter baumannii, a nosocomial pathogen with a role in the oral cavity

Actinetobacter baumannii is an important nosocomial pathogen that can cause a wide range of serious conditions including pneumonia, meningitis, necrotizing fasciitis and sepsis. It is also a major cause of wound infections in military personnel injured during the conflicts in Afghanistan and Iraq, leading to its popular nickname of 'Iraqibacter'. Contributing to its success in clinical settings is resistance to environmental stresses such as desiccation and disinfectants. Moreover, in recent years there has been a dramatic increase in the number of A. baumannii strains with resistance to multiple antibiotic classes. Acinetobacter baumannii is an inhabitant of oral biofilms, which can act as a reservoir for pneumonia and chronic obstructive pulmonary disease. Subgingival colonization by A. baumannii increases the risk of refractory periodontitis. Pathogenesis of the organism involves adherence, biofilm formation and iron acquisition. In addition, A. baumannii can induce apoptotic cell death in epithelial cells and kill hyphal forms of Candida albicans. Virulence factors that have been identified include pili, the outer membrane protein OmpA, phospholipases and extracellular polysaccharide. Acinetobacter baumannii can sense blue light through a blue-light sensing using flavin (BLUF) domain protein, BlsA. The resulting conformational change in BlsA leads to changes in gene expression, including virulence genes.

Cephalosporin resistance among animal-associatedEnterobacteria: a current perspective

Beta-lactam antimicrobials are an important class of drugs used for the treatment of infection. Resistance can arise by several mechanisms, including the acquisition of genes encoding beta-lactamases from other bacteria, alterations in cell membrane permeability and over expression of endogenous beta-lactamases. The acquisition of beta-lactamase resistance genes by both Salmonella and Escherichia coli appears to be on the rise, which may pose potential problems for the treatment of infections in both human and animal medicine. The prudent use of clinically important antimicrobials is therefore critical to maintain their effectiveness. Where possible, the use of newer generation cephalosporins should be limited in veterinary medicine.

CTX-M-type β-lactamases: a successful story of antibiotic resistance

Production of extended-spectrum β-lactamases (ESBLs) is the principal mechanism of resistance to oxyimino-cephalosporins evolved by members of the family Enterobacteriaceae. Among the several ESBLs emerged among clinical pathogens, the CTX-M-type enzymes have proved the most successful in terms of promiscuity and diffusion in different epidemiological settings, where they have largely replaced and outnumbered other types of ESBLs. Originated by the capture and mobilization of chromosomal β-lactamase genes of strains of Kluyvera species, the blaCTX-M genes have become associated with a variety of mobile genetic elements that have mediated rapid and efficient inter-replicon and cell-to-cell dissemination involving highly successful enterobacterial lineages (e.g. Escherichia coli ST131 and ST405, or Klebsiella pneumoniae CC11 and ST147) to yield high-risk multiresistant clones that have spread on a global scale. The CTX-Mβ-lactamase lineage exhibits a striking plasticity, with a large number of allelic variants belonging in several sublineages, which can be associated with functional heterogeneity of clinical relevance. This review article provides an update on CTX-M-type ESBLs, with focus on structural and functional diversity, epidemiology and clinical significance.

Variable within- and between-herd diversity of CTX-M cephalosporinase-bearing Escherichia coli isolates from dairy cattle

bla(CTX-M) beta-lactamases confer resistance to critically important cephalosporin drugs. Recovered from both hospital- and community-acquired infections, bla(CTX-M) was first reported in U.S. livestock in 2010. It has been hypothesized that veterinary use of cephalosporins in livestock populations may lead to the dissemination of beta-lactamase-encoding genes. Therefore, our objectives were to estimate the frequency and distribution of coliform bacteria harboring bla(CTX-M) in the fecal flora of Ohio dairy cattle populations. In addition, we characterized the CTX-M alleles carried by the isolates, their plasmidic contexts, and the genetic diversity of the bacterial isolates themselves. We also evaluated the association between ceftiofur use and the likelihood of recovering cephalosporinase-producing bacteria. Thirty fresh fecal samples and owner-reported ceftiofur use data were collected from each of 25 Ohio dairy farms. Fecal samples (n = 747) yielded 70 bla(CTX-M)-positive Escherichia coli isolates from 5/25 herds, 715 bla(CMY-2) E. coli isolates from 25/25 herds, and 274 Salmonella spp. from 20/25 herds. The within-herd prevalence among bla(CTX-M)-positive herds ranged from 3.3 to 100% of samples. Multiple pulsed-field gel electrophoresis (PFGE) patterns, plasmid replicon types, and CTX-M genes were detected. Plasmids with CTX-M-1, -15, and -14 alleles were clonal by restriction fragment length polymorphism (RFLP) within herds, and specific plasmid incompatibility group markers were consistently associated with each bla(CTX-M) allele. PFGE of total bacterial DNA showed similar within-herd clustering, with the exception of one herd, which revealed at least 6 different PFGE signatures. We were unable to detect an association between owner-reported ceftiofur use and the probability of recovering E. coli carrying bla(CTX-M) or bla(CMY-2).

Noncovalent complexes of an inactive mutant of CTX-M-9 with the substrate piperacillin and the corresponding product

We determined the crystal structure of an inactive Ser70Gly mutant of CTX-M-9 in complex with the bulky penicillin piperacillin at precovalent and posthydrolytic stages in the catalytic process. The structures obtained at high resolution were compared with the corresponding structures for the small penicillin benzylpenicillin and the bulky cephalosporin cefotaxime. The findings highlight the key role of the configuration of the carbon adjacent to the acylamino group of the side chain of β-lactams in the precovalent recognition of substrates.

Antibiotic resistance genes in the bacteriophage DNA fraction of environmental samples

Antibiotic resistance is an increasing global problem resulting from the pressure of antibiotic usage, greater mobility of the population, and industrialization. Many antibiotic resistance genes are believed to have originated in microorganisms in the environment, and to have been transferred to other bacteria through mobile genetic elements. Among others, β-lactam antibiotics show clinical efficacy and low toxicity, and they are thus widely used as antimicrobials. Resistance to β-lactam antibiotics is conferred by β-lactamase genes and penicillin-binding proteins, which are chromosomal- or plasmid-encoded, although there is little information available on the contribution of other mobile genetic elements, such as phages. This study is focused on three genes that confer resistance to β-lactam antibiotics, namely two β-lactamase genes (blaTEM and blaCTX-M9) and one encoding a penicillin-binding protein (mecA) in bacteriophage DNA isolated from environmental water samples. The three genes were quantified in the DNA isolated from bacteriophages collected from 30 urban sewage and river water samples, using quantitative PCR amplification. All three genes were detected in the DNA of phages from all the samples tested, in some cases reaching 104 gene copies (GC) of blaTEM or 102 GC of blaCTX-M and mecA. These values are consistent with the amount of fecal pollution in the sample, except for mecA, which showed a higher number of copies in river water samples than in urban sewage. The bla genes from phage DNA were transferred by electroporation to sensitive host bacteria, which became resistant to ampicillin. blaTEM and blaCTX were detected in the DNA of the resistant clones after transfection. This study indicates that phages are reservoirs of resistance genes in the environment.

Characterization of extended-spectrum beta-lactamases produced by Escherichia coli isolated from hospitalized and nonhospitalized patients: emergence of CTX-M-15-producing strains causing urinary tract infections

Extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli isolates were obtained from hospitalized and nonhospitalized patients in Belgium between August 2006 and November 2007. The antimicrobial susceptibility of these isolates was determined and their ESBL genes were characterized. Clonal relationships between the CTX-M-producing E. coli isolates causing urinary tract infections were also studied. A total of 90 hospital- and 45 community-acquired cephalosporin-resistant E. coli isolates were obtained. Tetracycline, enrofloxacine, gentamicin, and trimethoprim-sulfamethaxozole resistance rates were significantly different between the community-onset and hospital-acquired isolates. A high diversity of different ESBLs was observed among the hospital-acquired E. coli isolates, whereas CTX-M-15 was dominating among the community-acquired E. coli isolates (n = 28). Thirteen different pulsed-field gel electrophoresis profiles were observed in the community-acquired CTX-M-15-producing E. coli, indicating that multiple clones have acquired the bla(CTX-M-15) gene. All community-acquired CTX-M-15-producing E. coli isolates of phylogroups B2 and D were assigned to the sequence type ST131. The hospital-acquired CTX-M-15-producing E. coli isolates of phylogroups B2, B1, A, and D corresponded to ST131, ST617, ST48, and ST405, respectively. In conclusion, CTX-M-type ESBLs have emerged as the predominant class of ESBLs produced by E. coli isolates in the hospital and community in Belgium. Of particular concern is the predominant presence of the CTX-M-15 enzyme in ST131 community-acquired E. coli.

Structural insights into substrate recognition and product expulsion in CTX-M enzymes

beta-Lactamase-mediated resistance to beta-lactam antibiotics poses a major threat to our antibiotic armamentarium. Among beta-lactamases, a significant threat comes from enzymes that hydrolyze extended-spectrum cephalosporins such as cefotaxime. Among the enzymes that exhibit this phenotype, the CTX-M family is found worldwide. These enzymes have a small active site, which makes it difficult to explain how they hydrolyze the bulky extended-spectrum cephalosporins into the binding site. We investigated noncovalent substrate recognition and product release in CTX-M enzymes using steered molecular dynamics simulation and X-ray diffraction. An arginine residue located far from the binding site favors the capture and tracking of substrates during entrance into the catalytic pocket. We show that the accommodation of extended-spectrum cephalosporins by CTX-M enzymes induced subtle changes in the active site and established a high density of electrostatic interactions. Interestingly, the product of the catalytic reaction initiates its own release because of steric hindrances and electrostatic repulsions. This suggests that there exists a general mechanism for product release for all members of the beta-lactamase family and probably for most carboxypeptidases.

Extended-spectrum β-lactamase-producing Salmonella enterica serovar Oranienburg (CTX-M-2 group) in a pediatric hospital in Tucumán, Argentina

INTRODUCTION: Salmonella sp infections have been reported over recent years in hospitals in Argentina and other countries due to multiresistant strains. The aim of this study was to characterize the extended-spectrum β-lactamases in third-generation cephalosporin-resistant strains of Salmonella enterica serovar Oranienburg. METHODS: We studied 60 strains isolated from children with gastroenteritis and/or extraintestinal complications. The antibiotic susceptibility patterns of the isolates were analyzed and the β-lactamases were characterized using phenotyping and genotyping methods. RESULTS: All the strains were resistant to ampicillin, cefotaxime, cefepime and aztreonam and partially susceptible to ceftazidime, thus corresponding well with the resistance phenotype conferred by CTX-M-type β-lactamases. An isoelectric point enzyme (pI = 7.9) was detected in all of the strains, and this was confirmed by PCR as a member of the CTX-M-2 group. CONCLUSIONS: This is the first report of Salmonella enterica serovar Oranienburg producing β-lactamases of the CTX-M-2 group in a pediatric hospital in Tucumán, Argentina.

Changing prevalence of Escherichia coli with CTX-M-type extended-spectrum beta-lactamases in outpatient urinary E. coli between 2003 and 2008

One hundred ninety-three single-patient isolates of Escherichia coli harboring extended-spectrum beta-lactamases (ESBL) were identified among 11 407 E. coli urine isolates recovered from single-patient outpatient urine cultures from 2003 to 2008. The percentage of ESBL-producing E. coli among community-onset E. coli urine isolates increased from 0.21% in 2003 to 2.99% in 2008. One hundred seven of the ESBL producers were positive for the presence of bla(CTX-M) genes. The percentage of CTX-M-producing E. coli rose from 0.07% in 2003 to 1.66% in 2008. The annual percentage of ESBL E. coli producing CTX-Ms changed from 35% in 2003 to 64% in 2008. Genes belonging to 3 bla(CTX-M) groups: bla(CTX-M-1) group, bla(CTX-M-2) group, and bla(CTX-M)(-9) group, were detected. In addition, resistance to commonly used antimicrobial agents for community-acquired urinary tract infections was found common among CTX-M-producing E. coli isolates. Ertapenem and nitrofurantoin showed good in vitro activity against CTX-M producers.

Rapid characterization of beta-lactamases by multiplex PCR

The rising prevalence of the members of the Enterobacteriaceae, Pseudomonas spp. and Acinetobacter baumannii that produce extended-spectrum beta-lactamases (ESBLs) and carbapenem-hydrolysing beta-lactamases (carbapenemases) represents one of the largest "new" resistance problems faced by clinicians and microbiologists during the last 10 years. These diverse enzymes have emerged globally and represent serious health challenges, compromising therapeutic choice and complicating patient management. The rapid detection of strains that produce these beta-lactamases in clinical bacteriology laboratories allows appropriate therapy to be implemented promptly, which reduces patient mortality. This chapter describes three multiplex PCR assays, which may be used to detect genes that encode five families of CTX-M-type ESBLs (groups 1, 2, 8, 9, and 25), five families of metallo-carbapenemases (IMP, VIM, SPM, GIM, and SIM enzymes), and four families of OXA-carbapenemases (OXA-23-like, OXA-40-like, OXA-51-like, and OXA-58-like enzymes). The CTX-M ESBLs are the most prevalent of these enzyme groups, particularly, though not exclusively, in isolates of Escherichia coli and in Klebsiella spp.; metallo-carbapenemases are often found in Pseudomonas spp. and other "non-fermenters," but are also emerging problems in members of the Enterobacteriaceae in some countries and locales; with a few exceptions, the OXA-carbapenemases detected by the assay described are limited to isolates of Acinetobacter spp. These assays are suitable for deployment in national reference laboratories, but should also be considered for use in regional centres and in tertiary referral hospitals.

Updated functional classification of beta-lactamases

Two classification schemes for beta-lactamases are currently in use. The molecular classification is based on the amino acid sequence and divides beta-lactamases into class A, C, and D enzymes which utilize serine for beta-lactam hydrolysis and class B metalloenzymes which require divalent zinc ions for substrate hydrolysis. The functional classification scheme updated herein is based on the 1995 proposal by Bush et al. (K. Bush, G. A. Jacoby, and A. A. Medeiros, Antimicrob. Agents Chemother. 39:1211-1233, 1995). It takes into account substrate and inhibitor profiles in an attempt to group the enzymes in ways that can be correlated with their phenotype in clinical isolates. Major groupings generally correlate with the more broadly based molecular classification. The updated system includes group 1 (class C) cephalosporinases; group 2 (classes A and D) broad-spectrum, inhibitor-resistant, and extended-spectrum beta-lactamases and serine carbapenemases; and group 3 metallo-beta-lactamases. Several new subgroups of each of the major groups are described, based on specific attributes of individual enzymes. A list of attributes is also suggested for the description of a new beta-lactamase, including the requisite microbiological properties, substrate and inhibitor profiles, and molecular sequence data that provide an adequate characterization for a new beta-lactam-hydrolyzing enzyme.

Emergence of CTX-M-15 type extended-spectrum beta-lactamase-producing Salmonella spp. in Kuwait and the United Arab Emirates

Cephalosporins are major antimicrobials used to treat serious Salmonella infections. However, their effectiveness is being compromised by the emergence of extended-spectrum beta-lactamases (ESBLs). The genetic determinants encoding ESBL in Salmonella spp. isolated from patients in Kuwait and United Arab Emirates (UAE) were studied over a 2 year period. Out of a total of 407 isolates, 116 isolates possessed the resistance phenotypes consistent with possible ESBL production. Of these, 69 (59.5 %) were ESBL positive. PCR and sequencing were used to determine the genetic determinant(s) responsible for ESBL phenotypes. A total of 14 (12.1 %) and 29 (24.6 %) isolates were CTX-M-15 ESBL producers and TEM producers, respectively. Ten CTX-M-15 producers carried the insertion sequence ISEcpI gene. PFGE analysis revealed identical profiles in 4 of the 13 Kuwaiti strains. This study reports the presence of the bla(CTX-M-15) gene in Salmonella spp. and Salmonella enterica serotype Typhi from Kuwait and UAE for what is believed to be the first time. This is of great concern as the gene is also found in association with the ISEcpI gene, which may easily facilitate its spread. These isolates originated mostly from non-Kuwaiti Arabs rather than from people of Asian origin.

Acinetobacter baumannii: an emerging multidrug-resistant threat

Amid the recent attention focused on the growing impact of methicillin-resistant Staphylococcus aureus and multidrug-resistant Pseudomonas aeruginosa infections, the pathogen Acinetobacter baumannii has been stealthily gaining ground as an agent of serious nosocomial and community-acquired infection. Historically, Acinetobacter spp. have been associated with opportunistic infections that were rare and of modest severity; the last two decades have seen an increase in both the incidence and seriousness of A. baumannii infection, with the main targets being patients in intensive-care units. Although this organism appears to have a predilection for the most vulnerable patients, community-acquired A. baumannii infection is an increasing cause for concern. The increase in A. baumannii infections has paralleled the alarming development of resistance it has demonstrated. The persistence of this organism in healthcare facilities, its inherent hardiness and its resistance to antibiotics results in it being a formidable emerging pathogen. This review aims to put into perspective the threat posed by this organism in hospital and community settings, describes new information that is changing our view of Acinetobacter virulence and resistance, and calls for greater understanding of how this multifaceted organism came to be a major pathogen.

Extended-spectrum beta-lactamase-producing Enterobacteriaceae: an emerging public-health concern

The medical community relies on clinical expertise and published guidelines to assist physicians with choices in empirical therapy for system-based infectious syndromes, such as community-acquired pneumonia and urinary-tract infections (UTIs). From the late 1990s, multidrug-resistant Enterobacteriaceae (mostly Escherichia coli) that produce extended-spectrum beta lactamases (ESBLs), such as the CTX-M enzymes, have emerged within the community setting as an important cause of UTIs. Recent reports have also described ESBL-producing E coli as a cause of bloodstream infections associated with these community-onset UTIs. The carbapenems are widely regarded as the drugs of choice for the treatment of severe infections caused by ESBL-producing Enterobacteriaceae, although comparative clinical trials are scarce. Thus, more rapid diagnostic testing of ESBL-producing bacteria and the possible modification of guidelines for community-onset bacteraemia associated with UTIs are required.

Prevalence and clonality of extended-spectrum beta-lactamases in Asia

Asia is almost certainly a part of the world in which extended-spectrum beta-lactamases (ESBLs) have emerged de novo, with some early antimicrobial resistance studies showing high levels of the ESBL phenotype, particularly among Klebsiella, and most notably in China, Korea, Japan and India. There is a lack of genotyping studies but work from the late 1990s suggests that SHV-5 and SHV-12 were most common then, with only very rare reports of TEM-related ESBL genes. As in other parts of the world, quite marked differences have since been seen in the pattern of ESBL genes, particularly in relation to the CTX-M family. The early emergence of TOHO CTX-M-2 in Japan contrasted with CTX-M-3 and -14 in China and many other parts of the Far East, suggesting the separate transfer of genes from the genome of Kluyvera spp. to mobile genetic elements in human-associated Enterobacteriaceae. ESBL production rates are now very high compared with Europe. In most countries, there are mixtures of CTX-M types, with VEB appearing significantly in Vietnam and Thailand, and ESBL isolates from India being completely dominated by the presence of bla(CTX-M-15) alone, with no other CTX-M types reported. With the total population of India and China being c. 2.4 billion and with faecal carriage rates of, probably, c. 10%, these countries represent major reservoirs of bla(CTX-M) genes. Increasing international travel and trade will lead to the movement of many of these ESBL genes. The high prevalence of ESBL genes in Asia means that the empirical treatment of serious infections with beta-lactam antibiotics, except carbapenems, is seriously compromised.

Convergent in vivo and in vitro selection of ceftazidime resistance mutations at position 167 of CTX-M-3 beta-lactamase in hypermutable Escherichia coli strains

We report on a novel CTX-M extended-spectrum beta-lactamase (ESBL), designated CTX-M-42, with enhanced activity toward ceftazidime. CTX-M-42 was identified in a hypermutable Escherichia coli nosocomial isolate (isolate Irk2320) and is a Pro167Thr amino acid substitution variant of CTX-M-3. By molecular typing of ESBL-producing E. coli strains previously isolated in the same hospital ward, we were able to identify a putative progenitor (strain Irk1224) of Irk2320, which had a mutator phenotype and harbored the CTX-M-3 beta-lactamase. To reproduce the natural evolution of CTX-M-3, we selected for ceftazidime resistance mutations in bla CTX-M-3 gene in vitro both in clinical isolate Irk1224 and in laboratory-derived hypermutable (mutD5) strain GM2995. These experiments yielded CTX-M-3 Pro167Ser and CTX-M-3 Asn136Lys mutants which conferred higher levels of resistance to ceftazidime than to cefotaxime. CTX-M-3 Asn136Lys had a level of low activity toward ampicillin, which may explain its absence from clinical isolates. We conclude that the selection of CTX-M-42 could have occurred in vivo following treatment with ceftazidime and was likely facilitated by the hypermutable background.

An epidemic of plasmids? Dissemination of extended-spectrum cephalosporinases among Salmonella and other Enterobacteriaceae

CTX-M- and AmpC-type beta-lactamases comprise the two most rapidly growing populations among the extended-spectrum cephalosporinases. The evolution and dissemination of resistance genes encoding these enzymes occur mostly through the transmission of plasmids. The high prevalence of clinical isolates of Enterobacteriaceae producing the plasmid-mediated extended-spectrum cephalosporinases resembles an epidemic of plasmids, and has generated serious therapeutic problems. This review describes the emergence and worldwide spread of various classes of plasmid-mediated extended-spectrum cephalosporinases in Salmonella and other Enterobacteriaceae, the transfer mechanism of the plasmids, detection methods, and therapeutic choices.

Characterization of CTX-M-15-ProducingKlebsiella pneumoniaeandEscherichia coliStrains Isolated from Hospital Environments in Algeria

For detecting extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae in the hospital environment, sedimentation plates were placed in the rooms of two hospitals. Three environmental isolates, two Klebsiella pneumoniae, and one Escherichia coli resistant to extended-spectrum cephalosporins with a phenotype indicating CTX-M enzymes production (the minimum inhibitory concentration [MIC] of cefotaxime was higher than the MIC of ceftazidime) were recovered. By PCR and sequencing, the three isolates were found to produce CTX-M-15. The bla(CTX-M-15) genes in the three isolates were transferred by conjugation. One K. pneumoniae environmental isolate showed an identical and unique RAPD profile with two other K. pneumoniae clinical isolates recovered from urinary tract infection from patients hospitalized in two different wards of another hospital.

Spread of extended-spectrum beta-lactamase CTX-M-producing escherichia coli clinical isolates in community and nosocomial environments in Portugal

Of the 181 unduplicated Escherichia coli strains isolated in nine different hospitals in three Portuguese regions, 119 were extended-spectrum beta-lactamase (ESBL)-CTX-M producers and were selected for phenotype and genotype characterization. CTX-M producer strains were prevalent among community-acquired infections (56%), urinary tract infections (76%), and patients >/=60 years old (76%). In MIC tests, all strains were resistant to cefotaxime, 92% were resistant to ceftazidime, 93% were resistant to quinolones, 89% were resistant to aminoglycoside, and 26% were resistant to trimethoprim-sulfamethoxazole; all strains were sensitive to carbapenems, and 92% of the strains had a multidrug resistance phenotype. Molecular methods identified 109 isolates harboring a bla(CTX-M-15) gene, 1 harboring the bla(CTX-M-32) gene (first identification in the country), and 9 harboring the bla(CTX-M-14) gene. All isolates presented the ISEcp1 element upstream from the bla(CTX-M) genes; one presented the IS903 element (downstream of bla(CTX-M-14) gene), and none had the IS26 element; 85% carried bla(TEM-1B), and 84% also carried a bla(OXA-30). Genetic relatedness analysis based on pulsed-field gel electrophoresis defined five clusters and indicated that 76% of all isolates (from cluster IV) corresponded to a single epidemic strain. Of the 47 strains from one hospital, 41 belonged to cluster IV and were disseminated in three main wards. CTX-M-producing E. coli strains are currently a problem in Portugal, with CTX-M-15 particularly common. This study suggests that the horizontal transfer of bla(CTX-M) genes, mediated by plasmids and/or mobile elements, contributes to the dissemination of CTX-M enzymes to community and hospital environments. The use of extended-spectrum cephalosporins, quinolones, and aminoglycosides is compromised, leaving carbapenems as the therapeutic option for severe infections caused by ESBL producers.

Characterisation of KLUA-9, a β-lactamase from extended-spectrum cephalosporin-susceptible Kluyvera ascorbata, and genetic organisation of blaKLUA-9

This study characterised the genetic environment of the chromosomally encoded bla(KLUA-9) gene from a clinical Kluyvera ascorbata isolate and performed a kinetic characterisation of KLUA-9. Purified KLUA-9 showed the highest catalytic efficacies towards benzylpenicillin, ampicillin, piperacillin, first-generation cephalosporins, cefuroxime and cefoperazone; like other 'cefotaximases', it showed a much higher rate of hydrolysis of cefotaxime than ceftazidime, whilst dicloxacillin, cefoxitin and imipenem behaved as poor substrates. A 9kb insert from K. ascorbata was cloned (Escherichia coli KK68C1) and sequenced. bla(KLUA-9) and its 266bp upstream flanking region (almost identical to the integron-associated bla(CTX-M-2)) are preceded by an aspat variant, a ypdABC-like operon and two open reading frames with unknown functions. Unlike ISCR1-associated bla(CTX-M-2) genes, we failed to detect the putative orf513 recombination sites. Instead, we were able to localise the 5bp target sites for insertion of ISEcp1B, suggesting that this element could be responsible for future (or still undetected) mobilisation of bla(KLUA-9) to more efficiently transferred elements.

Biochemical characterisation of the CTX-M-14 β-lactamase

Cefotaxime-resistant Escherichia coli TUM1121 was isolated from an abscess of an 83-year-old patient. The CTX-M-14 gene was located on a 70 kb plasmid. The enzyme was purified and its activity was analysed. CTX-M-14 was poorly active against ceftazidime and aztreonam. Aztreonam behaved as a competitive inhibitor. Among the tested suicide substrates for class A beta-lactamases, sulbactam was a rather good substrate. Tazobactam and clavulanic acid behaved as inactivators. The interactions between clavulanic acid and CTX-M-14 were characterised by progressive inactivation of the beta-lactamase. Carbapenems such as imipenem, meropenem or doripenem did not behave as inactivators of CTX-M-14, however very small k(cat) values were observed. This result shows that CTX-M-14 is able to hydrolyse carbapenems.

Extended-spectrum β-lactamase-producing Shigella strains in Israel, 2000–2004

Routine susceptibility testing of 5,616 Shigella isolates at the National Shigella Reference Centre in Israel over a 5-year period (2000-2004) revealed resistance to ceftriaxone in one strain of Shigella boydii 2 and in two strains each of Shigella flexneri 2a, S. flexneri 6, and Shigella sonnei. All seven isolates were confirmed as producers of extended-spectrum beta-lactamase (ESBL) by the combination disk method, the Vitek 1 system, and a modification of the double-disk synergy test, which is based on the inhibitory properties of clavulanic acid, tazobactam, and sulbactam. Tazobactam had the strongest effect in all seven strains. Molecular characterization of the ESBLs identified CTX-M-type enzymes, consisting of the CTX-M-9 group (n = 3), CTX-M-3 (n = 2), CTX-M-39 (n = 1), and CTX-M-2 group (n = 1). Three of the strains also carried bla-(OXA) genes and a bla-(TEM) gene. Although the prevalence of ESBLs in this study was low, further research is needed on the spread and transfer of resistance genes, both in hospitals and in the community.

The emergence of antibiotic resistance by mutation

The emergence of mutations in nucleic acids is one of the major factors underlying evolution, providing the working material for natural selection. Most bacteria are haploid for the vast majority of their genes and, coupled with typically short generation times, this allows mutations to emerge and accumulate rapidly, and to effect significant phenotypic changes in what is perceived to be real-time. Not least among these phenotypic changes are those associated with antibiotic resistance. Mechanisms of horizontal gene spread among bacterial strains or species are often considered to be the main mediators of antibiotic resistance. However, mutational resistance has been invaluable in studies of bacterial genetics, and also has primary clinical importance in certain bacterial species, such as Mycobacterium tuberculosis and Helicobacter pylori, or when considering resistance to particular antibiotics, especially to synthetic agents such as fluoroquinolones and oxazolidinones. In addition, mutation is essential for the continued evolution of acquired resistance genes and has, e.g., given rise to over 100 variants of the TEM family of beta-lactamases. Hypermutator strains of bacteria, which have mutations in genes affecting DNA repair and replication fidelity, have elevated mutation rates. Mutational resistance emerges de novo more readily in these hypermutable strains, and they also provide a suitable host background for the evolution of acquired resistance genes in vitro. In the clinical setting, hypermutator strains of Pseudomonas aeruginosa have been isolated from the lungs of cystic fibrosis patients, but a more general role for hypermutators in the emergence of clinically relevant antibiotic resistance in a wider variety of bacterial pathogens has not yet been proven.

Real-time TaqMan PCR for rapid detection and typing of genes encoding CTX-M extended-spectrum β-lactamases

The prevalence of CTX-M-producing members of the Enterobacteriaceae is increasing worldwide. A novel, multiplex, real-time TaqMan PCR assay to detect and type bla CTX-M genes is described which is an improvement on previously described techniques with respect to reduced assay time, elimination of the need for protracted post-PCR processing and the convenience of a single reaction vessel. Based on β-lactam antibiogram and MIC data, 478 of 1279 Enterobacteriaceae isolates from clinical blood and urine culture specimens were selected and tested for extended-spectrum β-lactamase (ESBL) production using phenotypic methods. The new TaqMan assay detected and typed bla CTX-M genes in 21 of 28 ESBL-producing isolates.